Device for controlling the pressure of fabric pressure shoes on sewing machines or the like

ABSTRACT

An automatic control device that basically employs a pneumatic system that controls the pressure exerted on the shaft of the fabric pressure shoe, pressure that was traditionally exerted by spring systems or in any case mechanical-type systems that were always based on the pressure or the pull of a spring.  
     Basically automatic control device ( 1 ), installed above shaft ( 2 ) on which fabric pressure shoe ( 3 ) is mounted, consists of cylinder ( 4 ) in the chamber of which piston ( 5 ) slides.  
     The chamber of cylinder ( 4 ) is connected at the top to a tube ( 8 ) that leads to pneumatic control system ( 9 ). This system includes pressure regulator ( 10 ) of a type suitable for performing precision control of the pressure in the air circuit.

[0001] This industrial invention patent proposes a device for automatically controlling the pressure of fabric pressure shoes on preferably industrial-type sewing machines, meaning those equipped with claw, roller or belt conveying system or other similar conveying system.

[0002] It is an automatic control device that basically uses a pneumatic system for controlling the pressure exerted on the shaft of the fabric pressure shoe, pressure which was traditionally exerted by spring systems or in any case by mechanical-type systems that were always based on the pressure or the pull of a spring.

[0003] The automatic control device according to the invention, compared to known solutions, offers the basic advantage of having clearly improved thrust conditions on the fabric pressure shoes by greatly reducing inertia and by constantly maintaining correct working pressure at any speed and with any thickness of the fabric being processed.

[0004] As is known sewing machines, in their most common form, are machines that perform mechanical sewing of two pieces of fabric. In industrial sectors they are conceived according to different structural techniques depending on the various operations they are destined to perform.

[0005] Single or multi-needle machines are known, for example, used to sew garments such as jeans or casual pants in general, work clothes, shirts or even others.

[0006] These industrial sewing machines, based on their different versions, can sew on the widest variety of fabrics, on the yokes, on the rear or front crotch, on the leg felling or for the widest variety of applications. They come in special versions for light or extra-heavy fabrics with increased pressure shoe height and extended needle bar travel.

[0007] Normally all these versions are equipped with a fabric pressure shoe that carries a vertical shaft including a mechanical pressure device designed to absorb shoe shocks. This system is necessary both to compensate for the thrusts generated by different sewing speeds and, above all, to perform sewing on different thicknesses of fabric.

[0008]FIG. 1 illustrates one of-these traditional pressure devices. This device, as is shown, includes pin A equipped with head B in which spring C is inserted. Pin A slides in a special seat machined on shaft D of shoe E whereas the head of the pin itself is kept under pressure by presser F. The height of this presser can be adjusted by screwing pawl G.

[0009] It is clear that by tightening pawl G the spring will generate greater pressure on shoe E.

[0010] This structural technique, used to absorb shock forces on fabric pressure shoes in most if not all sewing machines, is not without practical problems. These are principally related to difficulties in controlling the pressure during work phases: in all cases, and these are the majority, where the machine encounters variations in the thickness of the fabric while it is sewing.

[0011] In these cases the spring pressure mechanisms do not adapt with the necessary precision to the needs of the fabric. This is because spring contrast mechanisms, as is well known, do not exert constant pressure during work phases but, on the contrary, generate an increase in pressure when their operating space is reduced.

[0012] This all has repercussions on the quality of sewing and on sewing speed. Speeds must sometimes be greatly reduced all to the detriment of manufacturing times and the cost of the finished product. The object of the invention is to have conceived and created a device for automatic control of fabric pressure shoe pressure that is able to overcome the above-indicated inconveniences. That is able, in other words, to maintain constant shoe operating pressure during all sewing phases.

[0013] The fabric pressure shoe control system that has been conceived and created, in conformity to one of the main goals of the invention, is able to keep shoe operating pressure constant during all sewing phases independent from the thickness of the fabric. This makes the machine able to work on any fabric at high sewing speeds.

[0014] The invention in question is based, as mentioned previously, on installation of a control device that uses a totally automatic pneumatic-type system. This offers the basic advantage of guaranteeing constant operating pressure following initial adjustment of the shoe at a certain work pressure.

[0015] The above-described objects and advantages are all achieved, according to the invention, by a device for automatic control of the fabric pressure shoe pressure on sewing machines, preferably industrial sewing machines, characterized by the fact that it employs a pneumatic system that includes at least one cylinder in which a piston slides, piston that is connected, through special connections, to the fabric pressure shoe shaft and by the fact that the inner chamber of said cylinder is connected, through suitable tubes, to a pneumatic control system that includes special pressure regulators equipped with stabilizing valves or the like with adjustable settings.

[0016] Other particular characteristics of the invention can be better understood by the following description, given as a non-exclusive example and given in reference to the attached drawing where:

[0017]FIG. 1 gives a schematic view of a traditional control system used to determine the pressure exerted by known fabric pressure shoes;

[0018]FIG. 2 gives a schematic view of the device as a whole according to the invention for automatic control of the pressure exerted by fabric pressure shoes for industrial sewing machines or the like;

[0019]FIG. 3 gives a detailed schematic view of the pneumatic control device.

[0020] In reference to these attached figures number 1 indicates the overall device according to the overall invention for automatic control of fabric pressure shoe pressure on industrial type sewing machines, meaning those equipped with claw, roller or belt conveying systems or any other similar conveying system.

[0021] Automatic control device 1, installed above shaft 2 on which fabric pressure shoe 3 is mounted, basically consists of cylinder 4 in which piston 5 slides.

[0022] As FIG. 2 shows piston 5, which is connected to shaft 2 of the shoe through arm 6, mounts, along its external edge, a ring groove suitable for housing elastic ring or “O-ring” seal 7 with a round and floating type cross-section.

[0023] Seal 7 is the type suited to exert “floating” sliding by the piston inside the cylinder chamber: sliding with minimum friction and without any possibility of sticking to or “gluing” to the cylinder sleeve.

[0024] The top part of the cylinder chamber is connected to tube 8 which terminates at pneumatic control system 9. A special pressure regulator 10 belongs to this control system. This regulator is designed to control the pressure of the air circuit with great precision. This control is executed and performed by pressure regulator 10 using a suitable reducing and stabilizing valve. The delivery rate of this valve can be varied using pressure regulator 11.

[0025] Compensation device 12 can if necessary be inserted between cylinder 4 and pressure regulator 10. This device compensates for small variations in pressure before it trips the pressure regulator's valve.

[0026] In its turn pressure regulator 13 is connected, through tube 13, to a pneumatic circuit that supplies the necessary amount of pressurized air.

[0027] It is possible, with this control system, to set a certain operating air pressure in the upper chamber of cylinder 4 and this will be kept constant in all conditions of thrust exerted by fabric pressure shoe 3's shaft 2, compensating for any variations in thrust caused by changes in fabric thickness or other thrusts caused by sewing speed.

[0028] While small pressure variations can be absorbed by compensation chamber 12, all substantial variations must be controlled and stabilized by pressure regulator 10 and by the reducing and stabilizing valve contained in it.

[0029] Lifting of the shoe when introducing and extracting the fabric is also done using a pneumatic control system. This performs suitable changes in the pressure exerted by the pneumatic system in the upper chamber of the cylinder.

[0030] Naturally the entire system is controlled by a computerized control system that determines and inputs all the different options and working parameters.

[0031] A second outlet, 14, is also provided for on the lower part of the cylinder. This has the advantage of being able to connect to an auxiliary pneumatic valve designed to help lift the shoe when introducing and extracting the fabric.

[0032] The automatic control system that has been described can be seen to clearly improve thrust conditions by fabric pressure shoes by greatly reducing inertia and maintaining correct working pressure constant at whatever speed and on whatever thickness of fabric being processed. The solution that has been described also illustrates the possibility of using arm 6 as a direct connection between the compensation device and the fabric pressure shoe shaft. But this connection can also be done in parallel with a suitable mechanical connection or joining component.

[0033] A technician in the sector can foresee several modifications and variants that can be brought to the device described and illustrated above as a non-exclusive example, offering solutions that are to be held to be included in the area of protection of the invention as defined by the following claims. 

1. Device for automatic control of the pressure exerted by the fabric pressure shoes of preferably industrial-type sewing machines characterized by the fact that it employs a pneumatic system that includes at least one cylinder (4) in which piston (5) slides, piston that is connected, through special connections (6) to shaft (2) of fabric pressure shoe (3) and by the fact that the inner chamber of said cylinder (4) is connected, by special tubes (8), to a pneumatic control system which includes special pressure regulators (10) equipped with stabilizing valves or the like with variable settings.
 2. Device for automatic control of the pressure exerted by fabric pressure shoes according to claim 1, characterized by the fact that said piston (5), which is connected to shaft (2) of the shoe through arm (6), is provided, along its outer edge, with a ring-shaped groove designed to house an elastic ring or “O-ring” seal (7) with a round and floating type cross section.
 3. Device for automatic control of the pressure exerted by fabric pressure shoes according to claim 1, characterized by the fact the cylinder chamber is connected at the top to a tube (8) which terminates at a pneumatic control system (9) that includes special pressure regulator (10) of the type designed to control the pressure in the air circuit with precision.
 4. Device for automatic control of the pressure exerted by fabric pressure shoes according to claim 1, characterized by the fact that this control is performed by pressure regulator (10) through a suitable pressure reducing and stabilizing valve and the delivery rate of this valve can be modified by pressure regulator (11).
 5. Device for automatic control of the pressure exerted by fabric pressure shoes according to claim 1, characterized by the fact that auxiliary compensation device (12) is inserted between said cylinder (4) and said pressure regulator (10) and compensates for small variations in pressure before causing the pressure regulator valve to operate.
 6. Device for automatic control of the pressure exerted by fabric pressure shoes according to claim 1, characterized by the fact that a second outlet (14) can be installed in the lower part of cylinder (4) to which an auxiliary pneumatic valve can be connected designed to help lift the shoe when introducing and extracting the fabric.
 7. Device for automatic control of the pressure exerted by fabric pressure shoes according to claim 1, characterized by the fact that the connection between said compensation device and said fabric pressure shoe shaft, performed using arm (6), can also be obtained in parallel with a suitable mechanical connection or joining component. 